Optical switch module and optical relay apparatus and path expansion method that use optical switch module

ABSTRACT

An optical switch module includes: N first input ports to which a signal is input; M first output ports from which a signal is output; an M×N switch to include N second input ports and M second output ports, and to set a path between the second input ports and the second output ports, the second output ports coupling with the first output ports, respectively; a test-signal input port to which a test-signal is capable of being externally input; an expansion port from which one of the test-signal and the signal from any one of the first input ports is output; and an optical switch to selectively connect at least one of the test-signal and the signal from any one of the first input ports to at least one of the expansion port and any one of the second input ports, wherein both N and M are natural numbers.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional application of prior U.S. applicationSer. No. 15/075,724 filed Mar. 21, 2016 which is based upon and claimsthe benefit of priority of the prior Japanese Patent Application No.:2015-093148, filed on Apr. 30, 2015, the entire contents of which areincorporated herein by reference.

FIELD

The embodiments discussed herein are related to an optical switch moduleand an optical relay apparatus and a path expansion method that use theoptical switch module.

BACKGROUND

A reconfigurable optical add/drop multiplexer (ROADM) used in awavelength division multiplex (WDM) system is an optical relay apparatusthat has optical switches to drop and add optical signals with differentwavelengths. To increase the flexibility of an optical network,implementation of Colorless, Directionless, and Contentionless (CDC)functions with which wavelengths and paths are freely set in a ROADM andwavelength contention is avoided is being studied. A ROADM having CDCfunctions is called a CDC-ROADM.

FIG. 1 illustrates the structure of a multicast switch (MCS) module 100as an example of an optical switching structure that implements CDCfunctions. At an MCS 110-2 on the drop side, which receives WDM signalsand drops optical signals, WDM signals received from M paths (deg 1 todeg M) are input to M1×N optical couplers (represented as SPLs inFIGS. 1) 13 ₁ to 13 _(m) (collectively referred to below as the opticalcouplers 13 at appropriate points) and are then dropped in N directions.The dropped WDM signals are connected to N M×1 optical switches 11 ₁ to11 _(n) (collectively referred to below as the optical switches 11 atappropriate points) and are then output from M×1 optical switches 11 ₁to 11 _(n) to N drop ports.

An MCS 110-1 on the add side, which adds, to WDM signals, opticalsignals to be transmitted, has the same structure as the MCS 110-2; atthe MCS 110-1, optical signals are input from N add parts into N 1×Moptical switches 11 ₁ to 11 _(n). Outputs from each 1×M optical switch11 are output to M N×1 optical couplers 13 ₁ to 13 _(m) and are thenoutput to M paths. The 1×M optical switches 11 on the add side and theM×1 optical switches 11 on the drop side have the same switch structure;they differ only in that the number of inputs and the number of outputsare reversed depending on the signal transmission direction. In FIG. 1,therefore, each of these optical switches is indicated as M×1 SW on boththe add side and the drop side. Similarly, the N×1 optical couplers 13on the add side and the 1×N optical couplers 13 on the drop side havethe same optical coupler structure; they differ only in that the numberof inputs and the number of outputs are reversed depending on the signaltransmission direction. In FIG. 1, therefore, each of these opticalcouplers is indicated as 1×N SPL on both the add side and the drop side.In this description, an optical switching structure having n outputports or input ports for m input ports or output ports will be referredto as M×N optical switch (including optical coupler, optical selector,optical splitter, and the like), regardless of the input and outputdirections.

In general, the MCS module 100 is used in such a way that the add sideand drop side are paired as illustrated in FIG. 1. An MCS having N addports or drop ports for M paths will be referred to as an M×N MCS.

FIG. 2 illustrates the node structure of a two-path ROADM 1001 in whichwavelength selective switches (WSSs) 105 a and 105 b and 2×2 MCSs 110-1and 110-2 are combined together. In a previous ROADM, arrayed waveguidegratings (AWGs) have been used at portions equivalent to the MCSs 110-1and 110-2, so it has been possible to input only optical signal with apredetermined wavelength from each add port. However, the use of theMCSs 110-1 and 110-2 enables an optical signal with a desired wavelengthto be input from each add port, so a Colorless function is achieved.This is also true on the drop side.

Optical output signals from two transponders 102 are input to signalinput ports. Paths for these optical output signals are selected by a2×2 MCS 110-1. Optical input signals from two paths are dropped to twotransponders 102 by a 2×2 MCS 110-2. Since a path can be selectedindependently for each signal, a Directionless function is achieved.With a wavelength assigned to an input port, it is also possible toinput a signal with the same wavelength from another input port(however, the same path is unable to be selected). That is, aContentionless function is achieved.

For a CDC-ROADM node, there is a demand to increase the number (M) ofselectable paths after an operation has been started. To meet thisdemand, at an MCS 210-2 on the drop side and an MCS 210-1 on the addside, each of 2×1 optical switches 12 ₁ to 12 _(n) (collectivelyreferred to below as the optical switches 12 at appropriate points) areconnected to one of the M×1 optical switches 11 ₁ to 11 _(n), as in anMCS module 200 illustrated in FIG. 3. Of the 2×1 optical ports 12, Nports not connected to the M×1 optical switches 11 are collectivelyconnected to an upgrade port 215 to increase the number of paths (seeU.S. Patent Application Publication No. 2013/0108215, for example).

SUMMARY

According to an aspect of the invention, an optical switch moduleincludes: N first input ports to which an optical signal is input; Mfirst output ports from which an optical signal is output; an M×N switchconfigured to include N second input ports and M second output ports,and to set an optical path between the N second input ports and the Msecond output ports, the M second output ports coupling with the M firstoutput ports, respectively; a test signal input port to which a testsignal is capable of being externally input; an expansion port fromwhich one of the test signal and the optical signal from any one of theN first input ports is output; and an optical switch configured toselectively connect at least one of the test signal and the opticalsignal from any one of the N first input ports to at least one of theexpansion port and any one of the N second input ports, wherein both Nand M are natural numbers.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates the structure of an ordinary MCS module;

FIG. 2 illustrates an example of the structure of a ROADM in which MCSmodules are used;

FIG. 3 illustrates an example of the structure of an MCS module withpath expansion functions;

FIG. 4 illustrates a connection structure after path expansion;

FIG. 5 illustrates a problem with a possible path expansion structure;

FIG. 6 illustrates a problem with another possible path expansionstructure;

FIG. 7 illustrates a path expansion structure in which MCS modules in afirst embodiment are used;

FIGS. 8A and 8B illustrate the states of 2×2 optical switches used inthe structure in FIG. 7;

FIG. 9 illustrates an example of the structure of a drop circuit usedfor optical connection check;

FIG. 10 illustrates connection check when the add side is operated;

FIG. 11 illustrates connections to added paths;

FIG. 12 illustrates a path expansion structure in which MCS modules in asecond embodiment are used;

FIG. 13 illustrates a modification of the second embodiment;

FIG. 14 illustrates a path expansion structure in which MCS modules in athird embodiment are used;

FIG. 15 illustrates a modification of the third embodiment;

FIG. 16 illustrates a path expansion structure in which MCS modules in afourth embodiment are used;

FIG. 17 illustrates a modification of the fourth embodiment;

FIG. 18 illustrates an example of the structure of a ROADM in which MCSmodules in an embodiment are used;

FIG. 19 illustrates a ROADM structure, in which path expansion has beencarried out; and

FIG. 20 illustrates a flowchart indicating a path expansion method in anembodiment.

DESCRIPTION OF EMBODIMENTS

FIG. 4 illustrates a structure in which an MCS module 200B, which is asecond MCS module in operation, is connected to an MCS module 200A,which is a first MCS module. An upgrade port 215A on the add side of theMCS 200A is connected to add ports in the MCS 200B through an opticalcable 217, and an upgrade port 215A on the drop side of the MCS 200A issimilarly connected to drop ports in the MCS 200B. When optical signalsare to be connected to paths of the second MCS 200B (or optical signalsare to be connected from paths of the MCS 200B), signal paths can beswitched toward the upgrade port 215A by switching 2×1 optical switches12 to the MCS 200B. During path expansion, only M paths have beenselectable for optical signals input from add ports. After pathexpansion, however, 2×M paths are selectable.

To increase paths by connecting a new MCS 200B, it is desirable to checkthat the MCS 200A in operation and the added MCS 200B are correctlyinterconnected. On the drop side, test signals can be input from anupgrade port 215B in the added MCS 200B. On the add side, however, thefirst MCS 200A is in operation, so it is difficult to send the testsignals to the MCS 200B. If the operation of the first MCS 200A isstopped to check connections, optical signal transmission is impeded.

Before explaining embodiments of the structures of optical switchmodules with which it is possible to check connections between anoptical switch module in operation and an optical switch module that isadded to increase paths on an optical network without affecting theoptical switch module in operation and explaining an embodiment of apath expansion method, problems with possible MCS module structures willdescribed with reference to FIGS. 5 and 6.

FIG. 5 is drawing to check connections between an MCS module 8A, whichis a first MCS module in operation, and an MCB module 8B, which is asecond MCS module connected to the MCS module 8A. The MCS modules 8A and8B have the same structure and the MCS module 8B is appropriately addedin response to a path expansion request. Therefore, the followingdescription will focus on the MCS module 8A. The MCS module 8A has anMCS 10 on the drop side and an MCS 210 on the add side. The MCS 210 onthe add side is the same as the MCS 210 in FIGS. 3 and 4. The MCS 10 onthe drop side has a test access port (TAP) circuit 19A between anupgrade port 15A and unused 2×1 optical switches 12. The TAP circuit 19Ahas n monitor photodetectors (PDs).

The upgrade port 15A on the add side of the MCS module 8A is connectedto the add ports of the second MCS module 8B through an optical cable27; the upgrade port 15A on the drop side is connected to the drop portsof the MCS module 8B through an optical cable 17. The optical cables 17and 27 are each, for example, an optical fiber connector with opticalconnectors. If a connection is disconnected due to a broken opticalfiber or a connection is made to an incorrect port due to, for example,an incorrect connection of an optical connector, no optical signal istransmitted between the MCS module 8A and the MCS module 8B.Alternatively, an optical signal is sent to an incorrect path.

On the drop side, test signals for connection monitoring are receivedfrom the upgrade port 15B of the second MCS module 8B to monitor thetest signals at the TAP circuit 19A in the first MCS module 8A. Even ifthe first MCS module 8A is in operation, connections to the second MCSmodule 8B can be checked.

On the add side, however, the first MCS module 8A is in operation, so itis difficult to input the test signals to the MCS 210 on the add side.To check connections on the add side, if the output ports of the 2×1optical switches 12 are switched to the upgrade port 15A to input thetest signals to the MCS 210 on the add side, optical transmission issuspended while the switching is in progress.

A similar problem arises in the structure in FIG. 6 as well. To increasepaths, MCS modules 9A and 9B in FIG. 6 use n (M+1)×1 optical switches 14instead of using n M×1 optical switches 11 and n 2×1 optical switches12. The MCS modules 9A and 9B have the same structure. Therefore, thefollowing description will focus on the MCS module 9A. The MCS module 9Ahas an MCS 70 on the drop side and an MCS 310 on the add side. In theMCS 70, an M+1st port of each optical switch 14 is connected to anupgrade port 75A and a TAP circuit 19 is inserted between the upgradeport 75A and the M+1st port of each optical switch 14. When test signalsfor connection monitoring are input from an upgrade port 75B of thesecond MCS module 9B, connections between the MCS module 9A and the MCSmodule 9B can be checked on the drop side. Since the optical switches 14₁ to 14 _(n) on the add side are in operation, however, it is difficultto receive the test signals on the add side.

In view of this situation, embodiments below will describe specificexamples of an MCS module with path expansion functions that, even if afirst MCS module is in operation, is capable of checking connectionswithout affecting the operation. In the description and drawings, likeelements will be denoted by like reference characters, and repeateddescriptions will be omitted.

First Embodiment

FIG. 7 schematically illustrates an MCS module 1 in a first embodiment.In the first embodiment, 2×2 optical switches 22 are used on the addside so that connections between an MCS module in operation and anadditional MCS module can be checked during path expansion.

The MCS module 1 has an MCS 20 on the add side and an MCS 10 on the dropside. The MCS 20 and MCS 10 may be structured by interconnecting opticalswitches and couplers through fibers. Alternatively, they may be of aplanar light wave circuit (PLC) type in which they are structured byusing waveguides made of quartz, silicon, or another semiconductormaterial.

The MCS 20 on the add side has n 2×2 optical switches 22 ₁ to 22 _(n)(collectively referred to below as the 2×2 optical switches 22 atappropriate points), which are disposed in correspondence to n addports, n M×1 optical switches 11, m 1×N optical couplers 13, a firstupgrade port 21, and a second upgrade port 25. An M×N switch thatinterconnects m paths and n ports in a selectable manner is structuredby using n M×1 optical switches 11 and m 1×N optical couplers 13.

One input port of each 2×2 optical switch 22 is connected to thecorresponding add port, and the other input port is connected to thefirst upgrade port 21. One output port of the 2×2 optical switch 22 isconnected to the corresponding M×1 optical switch 11, and the otheroutput port is connected to the second upgrade port 25. Both the firstupgrade port 21 and the second upgrade port 25 are formed by combining aplurality of ports. Test signals for connection monitoring are input tothe first upgrade port 21 as described later. In this sense, the firstupgrade port 21 may be referred to as the test signal input port 21. Thesecond upgrade port 25 passes the test signals through new paths tocheck connections and increases paths. In this sense, the second upgradeport 25 may be referred to as the expansion port 25.

FIGS. 8A and 8B illustrate the states of the 2×2 optical switch 22 usedin the MCS 20. The 2×2 optical switch 22 is an optical switch ofcrossbar type. In a straight state in FIG. 8A, an input port 1 isconnected to an output port 1 and an input port 2 is connected to anoutput port 2. In a cross state in FIG. 8B, the input port 1 isconnected to the output port 2 and the input port 2 is connected to theoutput port 1. During path expansion, the 2×2 optical switch 22 is inthe straight state, so an optical signal from the corresponding add portis input to the input port 1 and is output from the output port 1. Theinput port 2 and output port 2 are not used.

In a case as well in which connections are checked during pathexpansion, the 2×2 optical switch 22 is in the straight state. Anoptical signal is input from the corresponding add port to the inputport 1 and is output from the output port 1 to the corresponding M×1optical switch 11. A test signal for connection monitoring is input fromthe first upgrade port 21 and is then input to the input port 2 of the2×2 optical switch 22. The test signal is sent from the output port 2through the second upgrade port 25 to the additionally connected MCSmodule. When connections have been checked and optical signals are sentto the added paths, the 2×2 optical switches 22 are switched to thecross state. The states of the 2×2 optical switches 22 during connectioncheck and after path expansion will be described later in detail.

The MCS 10 on the drop side in the MCS module 1 is the same as the MCS10 in the MCS modules 8A and 8B in FIG. 5. Therefore, it is possible todetect test signals input from the upgrade port 15 in the additionallyconnected MCS module at the TAP circuit 19 in the MCS module 1 inoperation and conform connections.

FIG. 9 illustrates an example of the structure of the TAP circuit 19used in the MCS 10 on the drop side. The TAP circuit 19 has n monitorPDs 18 ₁ to 18 _(n) (collectively referred to below as the monitor PDs18 at appropriate points), which are disposed in a one-to-onecorrespondence to n optical fibers 16 ₁ to 16 _(n) (collectivelyreferred to below as the optical fibers 16 at appropriate points), whichextend from the upgrade port 15. Each monitor PD 18 monitors an opticalcomponent dropped from the corresponding optical fiber 16 and outputs acurrent according to the intensity of the test signal. If the intensityof the test signal detected by the monitor PD 18 is equal to or greaterthan a certain level, it can be decided that a connection to the MCSmodule used for path expansion has been established.

FIG. 10 illustrates connection check when the second MCS module 1B hasbeen connected to the first MCS module 1A. At the time of connectioncheck, each 2×2 optical switch 22 in the MCS 20 is in the straight state(see FIG. 8A). An optical signal is input from the corresponding addport to the first input port of the 2×2 optical switch 22, is outputfrom the first output port to the corresponding M×1 optical switch 11,and is transmitted to any one of M paths.

A test signal for connection monitoring is input from a first upgradeport 21A on the add side to the second input port of the 2×2 opticalswitch 22. The test signal is connected from the second output port to asecond upgrade port 25A on the add side, after which the test signal isled to a first upgrade port 21B on the add side in the second MCS module1B through the optical cable 27. The 2×2 optical switch 22 in the MCSmodule 1B is also in the straight state, so the test signal is monitoredat a second upgrade port 25B. By observing whether the test signal inputfrom the first upgrade port 21A on the add side in the first MCS module1A has been output to the second upgrade port 25B on the add side in thesecond MCS module 1B, a connection between the MCS module 1A and the MCSmodule 1B can be checked. Since n optical fibers in the first upgradeport 21A and first upgrade port 21B on the add side are connected to thecorresponding 2×2 optical switches 22, all n test signals can be checkedat the second upgrade port 25B on the add side in the second MCS module1B.

Although, in FIG. 10, the upgrade ports 15A, 15B, 25A, and 25B areschematically drawn with a plurality of lines, each of these ports maybe a plurality of ports connected to the optical cable 17 or 27 throughoptical connectors (not illustrated).

FIG. 11 illustrates signal transmission to paths that have been addedafter their connections had been confirmed. When an optical signal istransmitted to an added path, the corresponding 2×2 optical switches 22in both the MCS module 1A and MCS module 1B are switched to the crossstate. An optical signal from a transponder 102 (see FIG. 2) is inputfrom one add port in the MCS module 1A to the first input port of thecorresponding 2×2 optical switch 22, after which the optical signal isled from the second output port, which is diagonally opposite to thefirst input port, to the upgrade port 25A. The optical signal is inputto the first upgrade port 21B in the MCS 20 in the second MCS module 1Bthrough the optical cable 27, after which the optical signal is input tothe corresponding M×1 optical switch 11 by the corresponding 2×2 opticalswitch 22 in the cross state and is sent to any one of an M+1st path toa 2×Mth path.

When, on the drop side, an optical signal is to be supplied from anadded path to a transponder 102, the corresponding 2×1 optical switch 12in the first MCS 10 is switched to the upgrade port 15A and thecorresponding 2×1 optical switch 12 in the second MCS 10 is connected tothe corresponding M×1 optical switch 11. Thus, an optical signal thathas been sent from any one of the M+1st path to the 2×Mth path isreceived at the transponder 102.

When the MCS module 1B is added to the MCS module 1A for path expansionas described above, even if the first MCS module 1A is in operation,connections of optical paths between the MCS modules 1A and 1B can bechecked without affection the operation. After the connections have beenchecked, an optical signal can be sent to a desired path in a state inwhich there is no problem such as an incorrect connection or a brokenfiber.

Second Embodiment

FIG. 12 illustrates a path expansion structure in which MCS modules in asecond embodiment are used. An MCS module 2A is a module in operationand an MCS module 2B is an additionally connected module. In the secondembodiment, 2×2 optical switches 22 of crossbar type are used on thedrop side as well. In this structure, the drop side can lack a TAPcircuit.

The MCS modules 2A and 2B have the same structure. Therefore, thefollowing description will focus on the MCS module 2A. The MCS module 2Ahas an MCS 20-1 on the add side and an MCS 20-2 on the drop side. TheMCSs 20-1 and 20-2 have the same structure.

When connections are checked during path expansion, test signals areinput from the second upgrade port 25B in the MCS-20-2 in the second MCSmodule 2B. During connection check, the 2×2 optical switches 22 in boththe MCS modules 2A and 2B are in the straight state. The input testsignals are further input from the first upgrade port 21B in the MCS20-2 in the MCS module 2B to the second upgrade port 25A in the MCS 20-2in the MCS module 2A through the optical cable 17. The input testsignals are output to the first upgrade port 21A in the MCS 20-2 by the2×2 optical switches 22 and are monitored. This connection check can beperformed without affecting the operation of the first MCS module 2A.The structure and connection check on the add side are the same as inthe first embodiment.

When optical signals are sent to an M+1st path to a 2×Mth path afterconnection check, the 2×2 optical switches 22 in both the MCS 20-1 inthe MCS module 2A and the MCS 20-1 in the MCS module 2B are switched tothe cross state. When optical signals are received from the M+1st pathto the 2×Mth path on the drop side, the 2×2 optical switches 22 in boththe MCS 20-2 in the MCS module 2A and the MCS 20-2 in the MCS module 2Bare similarly switched to the cross state.

In this structure, it is possible to check connections of theadditionally connected MCS module 2B while the first MCS module 2A is inoperation. After the connections have been confirmed, optical signalscan be transmitted and received to and from added paths. In thestructure in FIG. 12, the add side and drop side can have the samestructure in each MCS module 2, so manufacturing is simplified. If MCSs20-1 and 20-2 of PLC type are used, cutouts of PLCs manufactured on thesame wafer can be used.

FIG. 13 illustrates a modification of the second embodiment. In FIG. 13,a TAP circuit is placed on at least one of the add side and drop sidefor connection check, besides the structure in FIG. 12. MCS modules 3Aand 3B have the same structure. Therefore, the following descriptionwill focus on the MCS module 3A.

The MCS module 3A has an MCS 30 on the add side and an MCS 40 on thedrop side. In the MCS 30, a TAP circuit 39A is placed between the firstupgrade port 21A and n 2×2 optical switches 22. In the MCS 40, the TAPcircuit 19A is placed between a second upgrade port 45A and n 2×2optical switches 22.

On the drop side, test signals are input from an upgrade port 45B in thesecond MCS module 3B and are then monitored at the TAP circuit 19A onthe drop side in the first MCS module 3A. On the add side, test signalsare input from the upgrade port 21A in the first MCS module 3A and arethen monitored at a TAP circuit 39B on the add side in the second MCSmodule 3B.

This structure enables the MCS modules themselves on an external addside and drop side to have optical signal monitoring functions forconnection check. Theoretically, even in a structure in which the TAPcircuit 39B is placed only in the MCS 30 in the second MCS module 3B onthe add side and the TAP circuit 19A is placed only in the MCS 40 in thefirst MCS module 3A on the drop side, connections can be checked. Fromthe viewpoint of achieving path expansion and connection check only byconnecting the MCS modules 3A and 3B having the same structure, however,a convenient way for path expansion is to use MCS modules of the sametype in which a TAP circuit is placed on both the add site and the dropside.

Third Embodiment

FIG. 14 illustrates a path expansion structure in which MCS modules in athird embodiment are used. In the third embodiment, 2×1 optical switches42 ₁ to 42 _(n) (collectively referred to below as the 2×1 opticalswitches 42 at appropriate points) and a verify port 51 are used on theadd side to check connections. An MCS module 4A is a module in operationand an MCS module 4B is an additionally connected module. In the examplein FIG. 14, the MCS modules 4A and 4B have the same structure.Therefore, the following description will focus on the MCS module 4A.

The MCS module 4A has an MCS 50 on the add side and the MCS 10 on thedrop side. The MCS 10 is the same as the MCS 10 in FIG. 7 (firstembodiment). That is, paths are added by using 2×1 optical switches 12and the upgrade port 15A, and connections are checked by using the TAPcircuit 19A.

The MCS 50 has n 2×1 optical switches 12, n M×1 optical switches 11, m1×N optical couplers 13, a TAP circuit 55A, and the verify port 51 usedto input test signals. The verify port 51 may be referred to as the testsignal input port 51. One output port of each 2×1 optical switch 12 isconnected to the corresponding M×1 optical switch 11, and a normal addoperation is performed.

The TAP circuit 55A has n 2×1 optical switches 42. Each 2×1 opticalswitch 42 has two input ports, one of which is used for a connection tothe corresponding 2×1 optical switch 12 and the other of which is usedfor a connection to the verify port 51.

When paths are to be added while the MCS module 4A, which is a first MCSmodule, is in operation, the MCS module 4B, which is a second MCSmodule, is connected with the optical cable 17 and optical cable 27. Onthe add side, an upgrade port 59A in the MCS module 4A is connected toadd ports in the MCS module 4B. To check connections, the input ports ofthe 2×1 optical switches 42 of the TAP circuit 55A in the MCS module 4Aare connected to the verify port 51, and test signals (optical signals)for connection monitoring are input from the verify port 51. These testsignals are led to the second MCS module 4B through the optical cable27.

In the second MCS module 4B, the 2×1 optical switches 12 used for pathselection are set so that input test signals are connected to theupgrade port 59B. The input port setting of each 2×1 optical switch 42in a TAP circuit 55B is switched to the corresponding 2×1 optical switch12. When it is confirmed that test signals are output from the upgradeport 59B, it is confirmed that optical paths on the add side have beenconnected between the first MCS module 4A and the second MCS module 4B.Upon the completion of the connection confirmation, the input portsetting of each 2×1 optical switch 42 in the TAP circuit 55A in thefirst MCS module 4A is switched back from the verify port 51 to thecorresponding 2×1 optical switch 12.

On the drop side, the upgrade port 15 in the MCS module 4A is connectedto the drop ports of the MCS module 4B. When connections are to bechecked, test signals are input from the upgrade port 15B in the secondMCS module 4B and the test signals are monitored at the TAP circuit 19Ain the first MCS module 4A, as in the first embodiment.

Theoretically, the MCS 50 in the second MCS module 4B can lack the TAPcircuit 55B and verify port 51; instead, the MCS 210 in FIG. 5 may beused. From the viewpoint of achieving path expansion and connectioncheck only by connecting MCS modules having the same structure, however,it is desirable to manufacture the MCS modules 4A and 4B having the samestructure and use them.

FIG. 15 illustrates a modification of the third embodiment. In thismodification, the TAP circuit 55A in which 2×1 optical switches 42 areused is placed in the drop side as well. An additional MCS module 5B isconnected to an MCS module 5A in operation for path expansion. In thisexample, the MCS modules 5A and 5B have the same structure. Therefore,the following description will focus on the MCS module 5A.

The MCS module 5A has an MCS 50-1 on the add side and an MCS 50-2 on thedrop side. When connections are to be checked on the drop side, thesetting of each 2×1 optical switch 42 is switched to the verify port 51at the TAP circuit 55A in the MCS 50-2 in the MCS module 5A, which is afirst MCS module. At the TAP circuit 55B in the MCS 50-2 in the MCSmodule 5B, which is a second MCS module, the setting of each 2×1 opticalswitch 42 is switched to the corresponding 2×1 optical switch 12.

Test signals are input from the upgrade port 15B in the second MCSmodule 5B, pass through drop ports in the MCS module 5B, are led to theupgrade port 15A in the first MCS module 5A through the optical cable17, and are input to the TAP circuit 55A. Since the setting of each 2×1optical switch 42 in the TAP circuit 55A has been switched to the verifyport 51, when an output optical signal is monitored at the verify port51, connections between the MCS modules 5A and 5B on the drop side arechecked. The structure and connection check on the add side are the sameas in FIG. 14.

In the structure in FIG. 15, the MCS 50-1 and MCS 50-2, which have thesame structure, can be used on the add side and drop side in each MCSmodule 5, the manufacturing process is simplified.

Fourth Embodiment

FIG. 16 illustrates a path expansion structure in which MCS modules in afourth embodiment are used. In the fourth embodiment, (M+1)×1 opticalswitches 14 are used for path expansion, instead of using a combinationof M×1 optical switches and 2×2 optical switches or 2×1 opticalswitches.

In this example, an MCS module 6A is a module in operation and an MCSmodule 6B is an additionally connected module. The MCS modules 6A and 6Bhave the same structure. Therefore, the following description will focuson the MCS module 6A.

The MCS module 6A has an MCS 60 on the add side and an MCS 70 on thedrop side. The MCS 60 has n (M+1)×1 optical switches 14 and m 1×Noptical couplers 13, a TAP circuit 55, and the verify port 51. M outputports of each (M+1)×1 optical switch 14 are connected to the 1×N opticalcouplers 13, and an M+1st output port is connected to the upgrade port59A. The TAP circuit 55 is inserted between the upgrade port 59A and theM+1st output port of each (M+1)×1 optical switch 14. The TAP circuit 55has n 2×1 optical switches 42. The first input port of each 2×1 opticalswitch 42 is connected to the M+1st output port of the corresponding(M+1)×1 optical switch 14, and the second input port is connected to theverify port 51. The output port of the 2×1 optical switch 42 isconnected to the upgrade port 59A.

The MCS 70 on the drop side has n (M+1)×1 optical switches 14, m 1×Noptical couplers 13, and the TAP circuit 19. M input ports of each(M+1)×1 optical switch 14 are connected to the 1×N optical couplers 13,and an M+1st input port is connected the upgrade port 45A. The TAPcircuit 19 is inserted between the upgrade port 45A and the M+1st inputport of each (M+1)×1 optical switch 14. The TAP circuit 19 has n monitorphotodetectors (PDs).

When paths are to be added, the MCS module 6B, which is a second MCSmodule, is connected to the MCS module 6A, which is a first MCS module,through the optical cables 17 and 27. When connections between them areto be checked, the settings of the 2×1 optical switches 42 in the TAPcircuit 55 in the first MCS module 6A are switched to the verify port 51on the add side and the settings of the 2×1 optical switch 42 in thesecond MCS module 6B are switched to the (M+1)×1 optical switches 14.When test signals are input from the verify port 51 in the first MCSmodule 6A and are monitored at the upgrade port 59B in the second MCSmodule 6B, connections between the first MCS module 6A and the secondMCS module 6B can be checked.

On the drop side, test signals are input from the upgrade port 45B inthe second MCS module 6B and are monitored at the TAP circuit 19 in thefirst MCS module 6A.

In this structure, connections can be checked on both the add side andthe drop side before path expansion, without affecting the operation ofthe first MCS module 6A.

FIG. 17 illustrates a modification of the fourth embodiment. In thismodification, the TAP circuit 55 in which 2×1 optical switches 42 areused is employed instead of the TAP circuit 19 in which PDs are used. Inthis example, an MCS module 7A is a module in operation and an MCSmodule 7B is an additionally connected module. The MCS module 7A and MCSmodule 7B have the same structure. Therefore, the following descriptionwill focus on the MCS module 7A.

The MCS module 7A has an MCS 60-1 on the add side and an MCS 60-2 on thedrop side. The MCS 60-1 has the same structure as the MCS 60 in FIG. 16,and the method of checking connections during path expansion is also thesame.

The MCS 60-2 has the same structure as the MCS 60-1. The MCS module 7B,which is a second MCS module, is connected to the MCS module 7A, whichis a first MCS module, through the optical cables 17 and 27, after whichconnections between them are checked. On the drop side, the output portsetting of each 2×1 optical switch 42 in the second MCS module 7B isswitched to the corresponding (M+1)×1 optical switch 14 and the outputport setting of each 2×1 optical switch 42 in the first MCS module 7A isswitched to the verify port 51. Test signals are input from the upgradeport 45B in the second MCS module 7B and are monitored at the verifyport 51 on the drop side in the first MCS module 7A.

In this structure as well, connections can be checked on both the addside and the drop side, without affecting the operation of the first MCSmodule 7A during path expansion.

Optical Relay Apparatus

FIG. 18 illustrates an example of the structure of a ROADM 80A in whichMCS modules in an embodiment and 1×9 WSSs 105 a and 105 b are combined.The MCS modules may be any one of the MCS modules 1 to 7 described inthe first to fourth embodiments and their modifications.

As an example, the MCS module 1 (or any one of MCS modules 2 to 7) is amodule that uses 4×4 MCSs having an upgrade function. For each installedtransponder (TRPN), adding and dropping are possible by using colorless,directionless, and contentionless (CDC) functions adaptable to up tofour paths.

The ROADM 80A is used on, for example, a ring network having six paths 1to 6. For optical signals transmitted from a path 1 on the drop side,the 1×9 WSSs 105 b on the drop side selects the four drop ports of theMCS module 1 (or any one of MCS modules 2 to 7) and five paths 2 to 6(or a network). Another WSS, which is not illustrated in FIG. 18 tosimplify it, selects optical signals sent from the add ports of the MCSmodule 1 (or any one of MCS modules 2 to 7) toward directions other thanthe path 1.

On the add side, optical signals destined for the path 1 are selected bythe 1×9 WSSs 105 a. For example, four inputs from the add ports of theMCS module 1 (or any one of MCS modules 2 to 7) and optical signals fromthe five paths 2 to 6 are selected. Another WSS, which is notillustrated in FIG. 18 to simplify it, selects signals to be droppedfrom the paths 2 to 6 to the MCS module 1 (or any one of MCS modules 2to 7).

FIG. 19 illustrates a ROADM 80B, in which path expansion has beencarried out, indicating an example of expansion in a case in whichadding and dropping adaptable to up to eight paths are desirable toincrease network flexibility in the MCS module 1 (or any one of MCSmodules 2 to 7). To increase the number of paths from 4 to 8, an upgradeport is used to connect a new MCS module 1B to the MCS module 1A inoperation. In a case as well in which any one of MCS modules 2A to 7A isused, the corresponding one of MCS modules 2B to 7B having the samestructure as the MCS modules 2A to 7A is additionally connected.

Although, in the examples of the structures in FIGS. 18 and 19, 4×4 MCSsand 1×9 WSSs have been used, M×N MCSs and 1×K WSSs (M, N, and K are anarbitrary integer) may be used instead.

FIG. 20 illustrates a flowchart indicating a path expansion method in anembodiment. First, a new MCS module (second MCS module, for example) tobe added to an MCS module in operation (first MCS module, for example)is prepared (S11). The first and second MCS modules may have any one ofthe structures described in the first to fourth embodiments.

The first MCS module and second MCS module are interconnected withoptical fibers such as in the form of an optical cable (S12). Settingsfor connection check are made at each MCS module on a demand basis(S13). If, for example, the TAP circuit 55 in which 2×1 optical switches42 are used is placed for connection check, it is checked whether thesettings of the 2×1 optical switches 42 in the first MCS module areswitched to the verify port 51 and the settings of the 2×1 opticalswitches 42 in the second MCS modules are switched to ports other thanthe verify port 51.

After the settings have been checked, optical signals (test signals) forconnection monitoring are input (S14), after which whether the testsignals have been monitored is checked (S15). If, for example, testsignals at a prescribed level or higher are detected (the result in S15is Yes), the processing is terminated, assuming that the test signalshave been confirmed. If the test signals fail to be confirmed (theresult in S15 is No), the connection states of the optical fibers andoptical connectors, for example, are checked (S16), and test signals areinput and checked again (S14 and S15). When S14 and S15 are repeateduntil the test signals are confirmed, reliable connection of theadditional MCS module is assured and it is suppressed that an opticalsignal is lost or is sent in an incorrect direction. Connection checkson the add site and drop side may be performed one at a time orsimultaneously.

Upon completion of connection confirmation, the second MCS module isoperated. Signals that have been sent from the transponders to M pathscan now be sent to 2×M paths. It also becomes possible for thetransponders to receive any optical signals from 2×M paths.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiments of the presentinvention have been described in detail, it should be understood thatthe various changes, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention.

What is claimed is:
 1. A path expansion method of a system including a first optical switch module and a second optical switch module, wherein both the first optical switch module and the second optical switch module includes N first input ports to which an optical signal is input, M first output ports from which an optical signal is output, an M×N switch configured to include N second input ports and M second output ports, and to set an optical path between the N second input ports and the M second output ports, the M second output ports coupling with the M first output ports, respectively, a test signal input port to which a test signal is capable of being externally input, an expansion port from which one of the test signal and the optical signal from any one of the N first input ports is output, and an optical switch configured to selectively connect at least one of the test signal and the optical signal from any one of the N first input ports to at least one of the expansion port and any one of the N second input ports, the path expansion method comprising: connecting the expansion port of the first optical switch module to the test signal input port of the second optical switch module; switching a setting of the optical switch of the first optical switch module so as to connect the test signal to the expansion port; monitoring, at the second optical switch module, the test signal input from the test signal input port of the first optical switch module, checking a connection between the first optical switch module and the second optical switch module, based on a result of the monitoring; and switching the setting of the optical switch of the first optical switch module so as to connect the optical signal from any one of the N first input ports to the expansion port, wherein both N and M are natural numbers.
 2. The path expansion method according to claim 1, wherein the optical switch is a 2×2 optical switch arranged between the N first input ports and the M×N switch, wherein a third input port of the 2×2 optical switch is coupled with any one of the N first input ports, a fourth input port of the 2×2 optical switch is coupled with the test signal input port, a third output port of the 2×2 optical switch is coupled with any one of the N second input ports, and a fourth output port of the 2×2 optical switch is coupled with the expansion port, wherein, when the test signal is input to the test signal input port, the third input port is switched to the third output port and the fourth input port is switched to the fourth output port, and wherein, when the optical signal from any one of the N first input ports is transmitted to the expansion port, the third input port is switched to the fourth output port and the fourth input port is switched to the third output port. 